The present invention relates to an apparatus for and method of non-destructively and simply determining properties of a surface acoustic wave (SAW) substrate such as a propagation speed or attenuation of surface acoustic waves in the SAW substrate.
A piezoelectric SAW substrate is produced from a wafer which is cut out of a piezoelectric monocrystalline rod. Since wafers cut out of one piezoelectric monocrystalline rod have different compositions, properties of those wafers which are not identical. Accordingly, SAW substrates produced from different wafers usually have different properties. For fabricating a SAW device provided with desired characteristics, it is necessary to determine beforehand properties of a SAW substrate, especially the propagation speed and attenuation of acoustic waves on the surface of the substrate.
In methods of simply determining properties of a piezoelectric SAW substrate without directly forming metal electrode finger patterns on the substrate, as shown in FIG. 1, a first set of interdigital fingers 1 and a second set of interdigital fingers 2 formed on a glass plate 21 are contacted to a to-be-determined piezoelectric SAW substrate 20. This is also described by M. B. Schulz et al. in J. Appl. Phys. 41, 2755, 1970. Otherwise, the first set of interdigital fingers and the second set of interdigital fingers are confronted by the to-be-determined SAW substrate with a spacing as described by M. K. Roy in J. Phys. E: Scientific Instruments 9, 148, 1976. Since these methods exhibit low efficiency conversion and coupling of surface acoustic waves, they cannot be applied to high precision determination of a propagation speed of surface acoustic waves.